If using raw cashews, preheat the oven to 350 degrees F. If using pre-roasted cashews you can skip this step. Spread the cashews in a single layer on a foil-covered baking sheet and roast until well toasted, approximately 5-7 minutes. Shake the baking sheet periodically for even roasting and keep an eye on them to make sure they don't burn. Allow them to cool.
In a double boiler, melt the bittersweet chocolate, stirring until smooth. Remove the chocolate from the double boiler and stir the cashews directly into the chocolate until well covered. You can also drizzle the chocolate over the nuts on the baking sheet for less coverage.
Spread the chocolate covered cashews evenly across the baking sheet (make sure it's still covered in foil for easy clean-up). Spread them out if possible.
Sprinkle the sea salt evenly over the nuts. Place them in the refrigerator until the chocolate hardens back up. Break up the nuts into small clusters.
I recommend starting with raw cashews for best results.